Electrical junctions were fabricated in sandwich configuration from Langmuir-Blodgett (LB) films of two types of material, -conjugated, peripherally substituted ring systems or a -bonded polymer. The sandwich junctions consisted of four to ten monolayers between two micro-structured gold electrodes, corresponding to a nominal film thickness between about 8 and 20 nm. At liquid helium temperature, the current (I)/voltage (V) characteristics generally exhibited smooth exponential behaviour or irregular steps. However, for a small fraction of the LB sandwiches comprising a -conjugated or -bonded compound, regular staircases were observed. It was possible to fit such characteristics with curves calculated on the basis of a Coulomb blockade model. These results are accounted for by the presence of nanometre-sized gold particles formed upon evaporation of the top electrode. Single electron tunnelling is assumed to proceed through double tunnel barrier junctions consisting of a gold island asymmetrically located between the top and bottom electrode.
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